rtnetlink: propagate error from dev_change_flags in do_setlink()

Andreas Henriksson <andreas@fatal.se> reported that unlike ifconfig,
iproute doesn't report an error when setting an interface up fails.

Propagate the return value from dev_change_flags() to fix this.

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a9a7721..ffde766 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -867,7 +867,9 @@ static int do_setlink(struct net_device *dev, struct ifinfomsg *ifm,
 		if (ifm->ifi_change)
 			flags = (flags & ifm->ifi_change) |
 				(dev->flags & ~ifm->ifi_change);
-		dev_change_flags(dev, flags);
+		err = dev_change_flags(dev, flags);
+		if (err < 0)
+			goto errout;
 	}
 
 	if (tb[IFLA_TXQLEN])